Formulations for oxidation protection of composite articles

ABSTRACT

The present disclosure includes carbon-carbon composite articles having oxidation protection coatings for limiting thermal and catalytic oxidation reactions and methods for applying oxidation protection coatings to carbon-carbon composite articles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. Ser. No. 14/671,637, filed Mar.27, 2015, and entitled “FORMULATIONS FOR OXIDATION PROTECTION OFCOMPOSITE ARTICLES,” which is incorporated by reference herein in itsentirety for all purposes.

FIELD OF INVENTION

The present disclosure related generally to carbon-carbon compositesand, more specifically, to oxidation protection systems forcarbon-carbon composite components.

BACKGROUND OF THE INVENTION

Oxidation protection systems for carbon-carbon composites are typicallydesigned to minimize loss of carbon material due to oxidation atoperating conditions, which include temperatures as high as 900° C.(1652° F.). Phosphate-based oxidation protection systems may reduceinfiltration of oxygen and oxidation catalysts into the composite.However, despite the use of such oxidation protection systems,significant oxidation of the carbon-carbon composites may still occurduring operation of components such as, for example, aircraft brakingsystems.

SUMMARY OF THE INVENTION

An article in accordance with various embodiments may comprise acarbon-carbon composite structure, an oxidation protection compositionincluding a base layer disposed on an outer surface of the carbon-carboncomposite structure and a sealing layer disposed on an outer surface ofthe base layer, wherein the base layer comprises a first phosphate glasscomposition having a boron nitride additive dispersed throughout thebase layer, and wherein the sealing layer comprises a second phosphateglass composition and is substantially free of boron nitride. The firstphosphate glass composition of the base layer may comprise between about10 weight percent and about 35 weight percent of the boron nitrideadditive, and further, between about 15 weight percent and about 30weight percent of the boron nitride additive. The first phosphate glasscomposition of the base layer may be represented by the formulaa(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z), where: A′ is selectedfrom: lithium, sodium, potassium, rubidium, cesium, and mixturesthereof; G_(f) is selected from: boron, silicon, sulfur, germanium,arsenic, antimony, and mixtures thereof; A″ is selected from: vanadium,aluminum, tin, titanium, chromium, manganese, iron, cobalt, nickel,copper, mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof; a is a number in the range from1 to about 5; b is a number in the range from 0 to about 10; c is anumber in the range from 0 to about 30; x is a number in the range fromabout 0.050 to about 0.500; y₁ is a number in the range from about 0.040to about 0.950; y₂ is a number in the range from 0 to about 0.20; and zis a number in the range from about 0.01 to about 0.5; (x+y₁+y₂+z)=1;and x<(y₁+y₂). The second phosphate glass composition of the sealinglayer may be represented by the formulaa(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z), where: A′ is selectedfrom: lithium, sodium, potassium, rubidium, cesium, and mixturesthereof; G_(f) is selected from: boron, silicon, sulfur, germanium,arsenic, antimony, and mixtures thereof; A″ is selected from: vanadium,aluminum, tin, titanium, chromium, manganese, iron, cobalt, nickel,copper, mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof; a is a number in the range from1 to about 5; b is a number in the range from 0 to about 10; c is anumber in the range from 0 to about 30; x is a number in the range fromabout 0.050 to about 0.500; y₁ is a number in the range from about 0.040to about 0.950; y₂ is a number in the range from 0 to about 0.20; and isa number in the range from about 0.01 to about 0.5; (x+y₁+y₂+z)=1; andx<(y₁+y₂). The second phosphate glass composition may further comprisean aluminum phosphate. The article may comprise a component of anaircraft wheel braking assembly.

A method for limiting oxidation in a composite structure in accordancewith various embodiments may comprise applying a base layer of a firstphosphate glass composition on an outer surface of a carbon-carboncomposite structure, wherein the base layer comprises between about 10weight percent and about 35 weight percent of a boron nitride, heatingthe carbon-carbon composite structure to a temperature sufficient toadhere the base layer to the carbon-carbon composite structure, applyinga sealing layer of a second phosphate glass composition on an outersurface of the base layer, wherein the second phosphate glasscomposition is substantially free of boron nitride, and heating thecarbon-carbon composite structure to a temperature sufficient to adherethe sealing layer to the base layer. The first phosphate glasscomposition of the base layer may comprise between about 15 weightpercent and about 30 weight percent of the boron nitride additive. Thefirst phosphate glass composition may be represented by the formulaa(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z), where: A′ is selectedfrom: lithium, sodium, potassium, rubidium, cesium, and mixturesthereof; G_(f) is selected from: boron, silicon, sulfur, germanium,arsenic, antimony, and mixtures thereof; A″ is selected from: vanadium,aluminum, tin, titanium, chromium, manganese, iron, cobalt, nickel,copper, mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof; a is a number in the range from1 to about 5; b is a number in the range from 0 to about 10; c is anumber in the range from 0 to about 30; x is a number in the range fromabout 0.050 to about 0.500; y₁ is a number in the range from about 0.040to about 0.950; y2 is a number in the range from 0 to about 0.20; and zis a number in the range from about 0.01 to about 0.5; (x+y1+y2+z)=1;and x<(y1+y2). The second phosphate glass composition may be representedby the formula a(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z): where: A′is selected from: lithium, sodium, potassium, rubidium, cesium, andmixtures thereof; G_(f) is selected from: boron, silicon, sulfur,germanium, arsenic, antimony, and mixtures thereof; A″ is selected from:vanadium, aluminum, tin, titanium, chromium, manganese, iron, cobalt,nickel, copper, mercury, zinc, thulium, lead, zirconium, lanthanum,cerium, praseodymium, neodymium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, actinium,thorium, uranium, yttrium, gallium, magnesium, calcium, strontium,barium, tin, bismuth, cadmium, and mixtures thereof; a is a number inthe range from 1 to about 5; b is a number in the range from 0 to about10; c is a number in the range from 0 to about 30; x is a number in therange from about 0.050 to about 0.500; y1 is a number in the range fromabout 0.040 to about 0.950; y₂ is a number in the range from 0 to about0.20; and z is a number in the range from about 0.01 to about 0.5;(x+y₁+y₂+z)=1; and x<(y₁+y₂). The second phosphate glass composition mayfurther comprise an aluminum phosphate. The method may further compriseforming a first slurry of the first phosphate glass composition bycombining a pulverized first phosphate glass matrix with a first carrierfluid and the boron nitride. Applying the base layer of the firstphosphate glass composition on the outer surface of the carbon-carboncomposite structure may comprise spraying or brushing the first slurryof the first phosphate glass composition to the carbon-carbon compositestructure.

The method may further comprise forming a second slurry of the secondphosphate glass composition by combining the second phosphate glasscomposition with a second carrier fluid, wherein applying the sealinglayer of the second phosphate glass composition on the base layercomprises spraying or brushing the second slurry of the second phosphateglass composition on the base layer. The second slurry may comprisebetween about 5.0 mol % and about 15 mol % ammonium dihydrogenphosphate. Prior to applying the base layer of the first phosphate glasscomposition to the carbon-carbon composite structure, a pretreatingcomposition may be applied to the outer surface of the carbon-carboncomposite structure, the pretreating composition comprising phosphoricacid and/or at least one acid phosphate salt, at least one aluminumsalt, and optionally at least one additional salt, the carbon-carboncomposite structure being porous, the pretreating compositionpenetrating at least some of a plurality of pores of the carbon-carboncomposite structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1A illustrates a cross sectional view of an aircraft wheel brakingassembly, in accordance with various embodiments;

FIG. 1B illustrates a partial side view of an aircraft wheel brakingassembly, in accordance with various embodiments;

FIG. 2 illustrates a method for limiting an oxidation reaction in acomposite substrate in accordance with various embodiments;

FIG. 3 illustrates experimental data obtained from testing various glasscompositions in accordance with various embodiments at varioustemperatures; and

FIG. 4 illustrates further experimental data obtained from testingvarious glass compositions in accordance with various embodiments at760° C. (1400° F.).

DETAILED DESCRIPTION

The detailed description of embodiments herein makes reference to theaccompanying drawings, which show embodiments by way of illustration.While these embodiments are described in sufficient detail to enablethose skilled in the art to practice the inventions, it should beunderstood that other embodiments may be realized and that logical andmechanical changes may be made without departing from the spirit andscope of the inventions. Thus, the detailed description herein ispresented for purposes of illustration only and not for limitation. Forexample, any reference to singular includes plural embodiments, and anyreference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected orthe like may include permanent, removable, temporary, partial, fulland/or any other possible attachment option.

With initial reference to FIGS. 1A and 1B, a wheel braking assembly 10such as may be found on an aircraft, in accordance with variousembodiments is illustrated. Aircraft wheel braking assembly may, forexample, comprise a bogie axle 12, a wheel 14 including a hub 16 and awheel well 18, a web 20, a torque take-out assembly 22, one or moretorque bars 24, a wheel rotational axis 26, a wheel well recess 28, anactuator 30, multiple brake rotors 32, multiple brake stators 34, apressure plate 36, an end plate 38, a heat shield 40, multiple heatshield sections 42, multiple heat shield carriers 44, an air gap 46,multiple torque bar bolts 48, a torque bar pin 50, a wheel web hole 52,multiple heat shield fasteners 53, multiple rotor lugs 54, and multiplestator slots 56. FIG. 1B illustrates a portion of aircraft wheel brakingassembly 10 as viewed into wheel well 18 and wheel well recess 28.

In various embodiments, the various components of aircraft wheel brakingassembly 10 may be subjected to the application of compositions andmethods for protecting the components from oxidation.

Brake disks (e.g., interleaved rotors 32 and stators 34) are disposed inwheel well recess 28 of wheel well 18. Rotors 32 are secured to torquebars 24 for rotation with wheel 14, while stators 34 are engaged withtorque take-out assembly 22. At least one actuator 30 is operable tocompress interleaved rotors 32 and stators 34 for stopping the aircraft.In this example, actuator 30 is shown as a hydraulically actuatedpiston, but many types of actuators are suitable, such as anelectromechanical actuator. Pressure plate 36 and end plate 38 aredisposed at opposite ends of the interleaved rotors 32 and stators 34.Rotors 32 and stators 34 can comprise any material suitable for frictiondisks, including ceramics or carbon materials, such as a carbon/carboncomposite.

Through compression of interleaved rotors 32 and stators 34 betweenpressure plates 36 and end plate 38, the resulting frictional contactslows rotation of wheel 14. Torque take-out assembly 22 is secured to astationary portion of the landing gear truck such as a bogie beam orother landing gear strut (not shown), such that torque take-out assembly22 and stators 34 are prevented from rotating during braking of theaircraft.

Carbon-carbon composites in the friction disks may operate as a heatsink to absorb large amounts of kinetic energy converted to heat duringslowing of the aircraft. Heat shield 40 may reflect thermal energy awayfrom wheel well 18 and back toward rotors 32 and stators 34. Withreference to FIG. 1A, a portion of wheel well 18 and torque bar 24 isremoved to better illustrate heat shield 40 and heat shield segments 42.With reference to FIG. 1B, heat shield 40 is attached to wheel 14 and isconcentric with wheel well 18. Individual heat shield sections 42 may besecured in place between wheel well 18 and rotors 32 by respective heatshield carriers 44 fixed to wheel well 18. Air gap 46 is definedannularly between heat shield segments 42 and wheel well 18.

Torque bars 24 and heat shield carriers 44 can be secured to wheel 14using bolts or other fasteners. Torque bar bolts 48 can extend through ahole formed in a flange or other mounting surface on wheel 14. Eachtorque bar 24 can optionally include at least one torque bar pin 50 atan end opposite torque bar bolts 48, such that torque bar pin 50 can bereceived through wheel web hole 52 in web 20. Heat shield sections 42and respective heat shield carriers 44 can then be fastened to wheelwell 18 by heat shield fasteners 53.

Under the operating conditions (e.g., high temperature) of aircraftwheel braking assembly 10, carbon-carbon composites may be prone tomaterial loss from oxidation of the carbon matrix. For example, variouscarbon-carbon composite components of aircraft wheel braking assembly 10may experience both catalytic oxidation and inherent thermal oxidationcaused by heating the composite during operation. In variousembodiments, composite rotors 32 and stators 34 may be heated tosufficiently high temperatures that may oxidize the carbon surfacesexposed to air. At elevated temperatures, infiltration of air andcontaminants may cause internal oxidation and weakening, especially inand around brake rotor lugs 54 or stator slots 56 securing the frictiondisks to the respective torque bar 24 and torque take-out assembly 22.Because carbon-carbon composite components of aircraft wheel brakingassembly 10 may retain heat for a substantial time period after slowingthe aircraft, oxygen from the ambient atmosphere may react with thecarbon matrix and/or carbon fibers to accelerate material loss. Further,damage to brake components may be caused by the oxidation enlargement ofcracks around fibers or enlargement of cracks in a reaction-formedporous barrier coating (e.g., a silicon-based barrier coating) appliedto the carbon-carbon composite.

Elements identified in severely oxidized regions of carbon-carboncomposite brake components include potassium (K) and sodium (Na). Thesealkali contaminants may come into contact with aircraft brakes as partof cleaning or de-icing materials. Other sources include salt depositsleft from seawater or sea spray. These and other contaminants (e.g. Ca,Fe, etc.) can penetrate and leave deposits in pores of carbon-carboncomposite aircraft brakes, including the substrate and anyreaction-formed porous barrier coating. When such contamination occurs,the rate of carbon loss by oxidation can be increased by one to twoorders of magnitude.

In various embodiments, components of aircraft wheel braking assembly 10may reach operating temperatures in the range from about 100° C. up toabout 900° C. However, it will be recognized that the oxidationprotection compositions and methods of the present disclosure may bereadily adapted to many parts in this and other braking assemblies, aswell as to other carbon-carbon composite articles susceptible tooxidation losses from infiltration of atmospheric oxygen and/orcatalytic contaminants.

With initial reference to FIG. 2, a method 200 for limiting an oxidationreaction (e.g., a thermal or a catalytic oxidation reaction) in acomposite substrate in accordance with various embodiments isillustrated. Method 200 may, for example, comprise applying an oxidationinhibiting composition to non-wearing surfaces of carbon-carboncomposite brake components. In various embodiments, method 200 may beused on the back face of pressure plate 36 and/or end plate 38, an innerdiameter (ID) surface of stators 34 including slots 56, as well as outerdiameter (OD) surfaces of rotors 32 including lugs 54. The oxidationinhibiting composition of method 200 may be applied to preselectedregions of a carbon-carbon composite that may be otherwise susceptibleto oxidation. For example, aircraft brake disks may have the oxidationinhibiting composition applied on or proximate stator slots 56 and/orrotor lugs 54.

In various embodiments, method 200 may comprise a pretreatment step 210.Step 210 may, for example, comprise applying a first pretreatingcomposition to the outer surface of a carbon-carbon composite, such as acomponent of aircraft wheel braking assembly 10. In various embodiments,the first pretreating composition comprises an aluminum oxide in water.For example, the aluminum oxide may comprise an additive, such as ananoparticle dispersion of aluminum oxide (for example, NanoBYK-3600®,sold by BYK Additives & Instruments). The first pretreating compositionmay further comprise a surfactant or a wetting agent. The carbon-carboncomposite may be porous, allowing the pretreating composition topenetrate at least some of the pores of the carbon-carbon composite.

In various embodiments, after applying the first pretreatingcomposition, the component is heated to remove water and fix thealuminum oxide in place. For example, the component may be heatedbetween about 100° C. (212° F.) and 200° C., and further, between 100°C. (212° F.) and 150° C. (392° F.).

Pretreatment step 210 may further comprise applying a second pretreatingcomposition. In various embodiments, the second pretreating compositioncomprises a phosphoric acid and an aluminum phosphate, aluminumhydroxide, or aluminum oxide. The second pretreating composition mayfurther comprise, for example, a second metal salt such as a magnesiumsalt. Further, the second pretreating composition may also comprise asurfactant or a wetting agent. In various embodiments, the secondpretreating composition is applied to the component atop the firstpretreating composition. The component may then, for example, be heated.In various embodiments, the component may be heated between about 600°C. (1112° F.) and about 800° C. (1472° F.), and further, between about650° C. (1202° F.) and 750° C. (1382° F.).

Method 200 may further comprise, for example, a step 220 of applying abase layer of a first phosphate glass to the carbon-carbon compositestructure. In various embodiments, the first phosphate glass compositioncomprises an acidic phosphate glass based on, for example, phosphoruspentoxide (P₂O₅).

The first phosphate glass composition may comprise a first phosphateglass matrix which is crushed and combined with one or more additionalcomponents to form the first phosphate glass composition. For example,the first phosphate glass matrix may comprise one or more alkali metalglass modifiers, one or more glass network modifiers and/or one or moreadditional glass formers. In various embodiments, boron oxide or aprecursor may optionally be combined with the P₂O₅ mixture to form aborophosphate glass, which has improved self-healing properties at theoperating temperatures typically seen in aircraft braking assemblies. Invarious embodiments, the phosphate glass and/or borophosphate glass maybe characterized by the absence of an oxide of silicon. Further, theratio of P₂O₅ to metal oxide in the fused glass may be in the range fromabout 0.25 to about 5.

Potential alkali metal glass modifiers may be selected from oxides oflithium, sodium, potassium, rubidium, cesium, and mixtures thereof. Incertain embodiments, the glass modifier may be an oxide of lithium,sodium, potassium, or mixtures thereof. These or other glass modifiersmay function as fluxing agents. Additional glass formers can includeoxides of boron, silicon, sulfur, germanium, arsenic, antimony, andmixtures thereof.

Suitable glass network modifiers include oxides of vanadium, aluminum,tin, titanium, chromium, manganese, iron, cobalt, nickel, copper,mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof.

The first phosphate glass matrix may be prepared by combining the aboveingredients and heating them to a fusion temperature. In certainembodiments, depending on the particular combination of elements, thefusion temperature can be in the range from about 700° C. (1292° F.) toabout 1500° C. (2732° F.). The melt may then be cooled and pulverized toform a frit or powder. In various embodiments, the first phosphate glassmatrix may be annealed to a rigid, friable state prior to beingpulverized. Glass transition temperature (T_(g)), glass softeningtemperature (T_(s)) and glass melting temperature (T_(m)) may beincreased by increasing refinement time and/or temperature. Beforefusion, the first phosphate glass matrix comprises from about 20 mol %to about 80 mol % of P₂O₅. In various embodiments, the first phosphateglass matrix comprises from about 30 mol % to about 70 mol % P₂O₅, orprecursor thereof. In various embodiments, the first phosphate glassmatrix comprises from about 40 to about 60 mol % of P₂O₅.

The first phosphate glass matrix can comprise from about 5 mol % toabout 50 mol % of the alkali metal oxide. In various embodiments, thefirst phosphate glass matrix comprises from about 10 mol % to about 40mol % of the alkali metal oxide. Further, the first phosphate glassmatrix comprises from about 15 to about 30 mol % of the alkali metaloxide or one or more precursors thereof. In various embodiments, thefirst phosphate glass matrix can comprise from about 0.5 mol % to about50 mol % of one or more of the above-indicated glass formers. The firstphosphate glass matrix may comprise about 5 to about 20 mol % by weightof one or more of the above-indicated glass formers. As used herein, mol% is defined as the number of moles of a constituent per the total molesof the solution.

In various embodiments, the first phosphate glass matrix can comprisefrom about 0.5 mol % to about 40 mol % of one or more of theabove-indicated glass network modifiers. The first phosphate glassmatrix may comprise from about 2.0 mol % to about 25 mol % of one ormore of the above-indicated glass network modifiers.

In various embodiments, the first phosphate glass matrix may representedby the formula:a(A′₂O)_(x)(P₂O₅)_(y1) b(G_(f)O)_(y2) c(A″O)_(z)  [1]

In Formula 1, A′ is selected from: lithium, sodium, potassium, rubidium,cesium, and mixtures thereof; G_(f) is selected from: boron, silicon,sulfur, germanium, arsenic, antimony, and mixtures thereof; A″ isselected from: vanadium, aluminum, tin, titanium, chromium, manganese,iron, cobalt, nickel, copper, mercury, zinc, thulium, lead, zirconium,lanthanum, cerium, praseodymium, neodymium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,actinium, thorium, uranium, yttrium, gallium, magnesium, calcium,strontium, barium, tin, bismuth, cadmium, and mixtures thereof; a is anumber in the range from 1 to about 5; b is a number in the range from 0to about 10; c is a number in the range from 0 to about 30; x is anumber in the range from about 0.050 to about 0.500; y₁ is a number inthe range from about 0.040 to about 0.950; y₂ is a number in the rangefrom 0 to about 0.20; and z is a number in the range from about 0.01 toabout 0.5; +y₁+y₂+z)=1; and x<(y₁+y₂). The first phosphate glass matrixmay be formulated to balance the reactivity, durability and flow of theresulting glass barrier layer for optimal performance.

In various embodiments, crushed first phosphate glass matrix is combinedwith additional components to form the first phosphate glasscomposition. For example, crushed first phosphate glass matrix may becombined with ammonium hydroxide, ammonium dihydrogen phosphate,nanoplatelets (such as graphene-based nanoplatelets), among others. Forexample, graphene nanoplatelets could be added to the crushed firstphosphate glass matrix. In various embodiments, the additionalcomponents may be combined and preprocessed before combining them withcrushed the first phosphate glass matrix. Other suitable additionalcomponents include, for example, surfactants.

In various embodiments, the first phosphate glass composition mayfurther comprise a boron nitride additive. For example, a boron nitride(such as hexagonal boron nitride) may be added to the first phosphateglass composition such that the resulting composition comprises betweenabout 10 weight percent and about 30 weight percent of boron nitride.Further, the composition may comprise between about 15 weight percentand 25 weight percent of boron nitride. Boron nitride may be preparedfor addition to the first phosphate glass composition by, for example,ultrasonically exfoliating the boron nitride in dimethylformamide (DMF),a solution of DMF and water, or 2-propanol solution. In variousembodiments, the boron nitride additive may comprise a boron nitridethat has been prepared for addition to the first phosphate glasscomposition by crushing or milling (e.g., ball milling) the boronnitride. The resulting boron nitride may be combined with pulverizedfirst phosphate glass matrix (e.g., a frit or powder) in a first carrierfluid (such as, for example, water) to form a slurry, such as, forexample, a first slurry.

Step 220 may comprise, for example, spraying or brushing the firstslurry of the first phosphate glass composition on to the outer surfaceof the carbon-carbon composite structure. Any suitable manner ofapplying the base layer to carbon-carbon composite is within the scopeof the present disclosure.

In various embodiments, method 200 further comprises a step 230 ofheating the carbon-carbon composite structure to adhere the base layerto the carbon-carbon composite structure. The treated carbon-carboncomposite may be heated (e.g., dried or baked) at a temperature in therange from about 200° C. (292° F.) to about 1000° C. (1832° F.). Invarious embodiments, the composite is heated to a temperature in a rangefrom about 600° C. (1112° F.) to about 1000° C. (1832° F.), or betweenabout 200° C. (292° F.) to about 900° C. (1652° F.), or further, betweenabout 400° C. (752° F.) to about 850° C. (1562° F.). Step 230 may, forexample, comprise heating the carbon-carbon composite structure for aperiod between about 0.5 hour and about 8 hours.

In various embodiments, the composite may be heated to a first, lowertemperature (for example, about 30° C. (86° F.) to about 300° C. (572°F.)) to bake or dry the base layer at a controlled depth. A second,higher temperature (for example, about 300° C. (572° F.) to about 1000°C. (1832° F.)) may then be used to form a deposit from the base layerwithin the pores of the carbon-carbon composite. The duration of eachheating step can be determined as a fraction of the overall heating timeand can range from about 10% to about 50%. In various embodiments, theduration of the lower temperature heating step(s) can range from about20% to about 40% of the overall heating time. The lower temperaturestep(s) may occupy a larger fraction of the overall heating time, forexample, to provide relatively slow heating up to and through the firstlower temperature. The exact heating profile will depend on acombination of the first temperature and desired depth of the dryingportion.

Step 230 may be performed in an inert environment, such as under ablanket of inert gas (e.g., nitrogen, argon, and the like). For example,a carbon-carbon composite may be pretreated or warmed prior toapplication of the base layer to aid in the penetration of the baselayer. Step 230 may be for a period of about 2 hours at a temperature ofabout 750° C. (1382° F.) to about 800° C. (1472° F.). The carbon-carboncomposite and base layer may then be dried or baked in a non-oxidizing,inert or mostly inert atmosphere, e.g., noble gasses and/or nitrogen(N₂), to optimize the retention of the first phosphate glass compositionof the base layer in the pores. This retention may, for example, beimproved by heating the carbon-carbon composite to about 200° C. (392°F.) and maintaining the temperature for about 1 hour before heating thecarbon-carbon composite to a temperature in the range described above.The temperature rise may be controlled at a rate that removes waterwithout boiling, and provides temperature uniformity throughout thecarbon-carbon composite.

Method 200 may further comprise a step 240 of applying a sealing layerof a second phosphate glass composition on an outer surface of the baselayer. In various embodiments, the second phosphate glass composition issubstantially free of boron nitride. In this case, “substantially free”means less than 0.01 percent by weight. For example, the secondphosphate glass composition may comprise any of the glass compositionsdescribed in connection with the first phosphate glass composition,without the addition of a boron nitride additive. In variousembodiments, the second phosphate glass composition may comprise thesame reactive phosphate glass matrix used to prepare the first phosphateglass composition. In other embodiments, the second phosphate glasscomposition comprises a different reactive phosphate glass matrix fromthe first phosphate glass matrix.

Similarly to step 220, step 240 may comprise preparing a secondphosphate glass composition slurry by combining the second phosphateglass composition with a second carrier fluid (such as, for example,water). Further, step 240 may comprise spraying or brushing slurry ofthe second phosphate glass composition on to the outer surface of thebase layer. Any suitable manner of applying the sealing layer to thebase layer is within the scope of the present disclosure

Method 200 may further comprise a step 250 of heating the carbon-carboncomposite structure to adhere the sealing layer to the base layer.Similarly to step 230, the carbon-carbon composite structure may beheated at a temperature sufficient to adhere the sealing layer to thebase layer by, for example, drying or baking the carbon-carbon compositestructure at a temperature in the range from about 200° C. (392° F.) toabout 1000° C. (1832° F.). In various embodiments, the composite isheated to a temperature in a range from about 600° C. (1112° F.) toabout 1000° C. (1832° F.), or between about 200° C. (392° F.) to about900° C. (1652° F.), or further, between about 400° C. (752° F.) to about850° C. (1562° F.), wherein in this context, the term “about”means+/−10° C. Further, step 250 may, for example, comprise heating thecarbon-carbon composite structure for a period between about 0.5 hourand about 8 hours, where the term “about” in this context onlymeans+/−0.25 hours.

In various embodiments, step 250 may comprise heating the composite afirst, lower temperature (for example, about 30° C. (86° F.) to about300° C. (572° F.)) followed by heating at a second, higher temperature(for example, about 300° C. (572° F.) to about 1000° C. (1832° F.)).Further, step 250 may be performed in an inert environment, such asunder a blanket of inert or mostly inert gas (e.g., nitrogen, argon, andthe like).

Table 1 illustrates a variety of phosphate glass compositions inaccordance with various embodiments.

TABLE 1 Phosphate Glass Composition A B C D E F Wt % Glass Matrix 75.0175.01 76.71 69.74 80.2 73.22 Wt % Boron Nitride 0 0 21.07 28.09 17.5324.54 Wt % o-AlPO4 0 2.27 0 0 0 0

Phosphate glass compositions A and B comprise boron nitride-freephosphate glasses. For example, glasses A and B may be suitable sealinglayers, such as the sealing layer applied in step 240 of method 200.Phosphate glass compositions C-F comprise boron nitride-containingphosphate glass. For example, glass compositions C-F may illustratesuitable base layers, such as base layers applied in step 220 of method200. As illustrated, the boron nitride content of glass compositions C-Fvaries between about 17.53 and 28.09 weight percent boron nitride.However, any suitable boron nitride-containing phosphate glass (asdescribed above) is in accordance with the present disclosure.

With reference to FIG. 3 and Table 2 (below), experimental data obtainedfrom testing various glass compositions in accordance with variousembodiments is illustrated.

TABLE 2 Base Layer (none) E D C F Sealing Layer A A A A A ExposureOxidation Temp Time (Hours) Percentage Weight Loss 675 Degrees C. 0 0.000.00 0.00 0.00 0.00 4 0.90 0.32 0.41 0.44 0.18 8 1.98 0.70 1.01 1.070.39 12 3.13 1.19 1.76 1.95 0.64 16 4.41 1.80 2.56 2.98 0.95 20 5.942.52 3.56 4.65 1.31 24 7.48 3.41 4.73 6.29 1.76 760 Degrees C. 26 10.634.31 6.43 8.47 2.11 28 14.28 5.40 8.37 11.13 2.54 870 Degrees C. 3024.43 7.18 11.96 15.95 3.50 32 36.45 12.76 17.27 23.43 6.89

As illustrated in Table 2, oxidation protection systems comprising abase layer of boron nitride-comprising glass compositions B-E andsealing layer A exhibited a lower weight loss to oxidation attemperatures at and above 675° C. (1250° F.) than sealing layer A byitself. Further, with reference to FIG. 4, a number of combinations areillustrated, including various combinations of pre-treatment (such as,for example, step 210), base layers, and sealing layers. For example,FIG. 4 illustrates the performance of a composition comprising a baselayer of glass composition F and a sealing layer B provides improvedoxidation protection over sealing layer A itself. Other combinationsinclude a base layer of glass composition F and a sealing layer B(without pre-treatment), and a base layer of F with a sealing layer of A(without pre-treatment).

Benefits and other advantages have been described herein with regard tospecific embodiments. Furthermore, the connecting lines shown in thevarious figures contained herein are intended to represent exemplaryfunctional relationships and/or physical couplings between the variouselements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in apractical system. However, the benefits, advantages, solutions toproblems, and any elements that may cause any benefit, advantage, orsolution to occur or become more pronounced are not to be construed ascritical, required, or essential features or elements of the disclosure.The scope of the disclosure is accordingly to be limited by nothingother than the appended claims, in which reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather “one or more.” Moreover, where a phrase similar to“at least one of A, B, or C” is used in the claims, it is intended thatthe phrase be interpreted to mean that A alone may be present in anembodiment, B alone may be present in an embodiment, C alone may bepresent in an embodiment, or that any combination of the elements A, Band C may be present in a single embodiment; for example, A and B, A andC, B and C, or A and B and C.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,” “anexample embodiment,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f), unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises,”“comprising,” or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

What is claimed is:
 1. A method for limiting an oxidation reaction in acomposite substrate, comprising: applying a base layer comprising afirst phosphate glass composition on an outer surface of a carbon-carboncomposite structure, wherein the first phosphate glass compositioncomprises a plurality of graphene nanoplatelets and a boron nitrideadditive; and heating the carbon-carbon composite structure to atemperature sufficient to adhere the base layer to the carbon-carboncomposite structure.
 2. The method of claim 1, wherein the firstphosphate glass composition of the base layer comprises between about 15weight percent and about 30 weight percent the boron nitride additive.3. The method of claim 1, wherein the first phosphate glass compositionis represented by the formulaa(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z): A′ is selected from:lithium, sodium, potassium, rubidium, cesium, and mixtures thereof;G_(f) is selected from: boron, silicon, sulfur, germanium, arsenic,antimony, and mixtures thereof; A″ is selected from: vanadium, aluminum,tin, titanium, chromium, manganese, iron, cobalt, nickel, copper,mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof; a is a number in the range from1 to about 5; b is a number in the range from 0 to about 10; c is anumber in the range from 0 to about 30; x is a number in the range fromabout 0.050 to about 0.500; y₁ is a number in the range from about 0.040to about 0.950; y₂ is a number in the range from 0 to about 0.20; and zis a number in the range from about 0.01 to about 0.5; (x+y₁+y₂+z)=1;and x<(y₁+y₂).
 4. The method of claim 1, further comprising: applying asealing layer comprising a second phosphate glass composition on anouter surface of the base layer, wherein the second phosphate glasscomposition is substantially free of boron nitride; and heating thecarbon-carbon composite structure to a temperature sufficient to adherethe sealing layer to the base layer.
 5. The method of claim 4, whereinthe second phosphate glass composition is represented by the formulaa(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z): A′ is selected from:lithium, sodium, potassium, rubidium, cesium, and mixtures thereof;G_(f) is selected from: boron, silicon, sulfur, germanium, arsenic,antimony, and mixtures thereof; A″ is selected from: vanadium, aluminum,tin, titanium, chromium, manganese, iron, cobalt, nickel, copper,mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof; a is a number in the range from1 to about 5; b is a number in the range from 0 to about 10; c is anumber in the range from 0 to about 30; x is a number in the range fromabout 0.050 to about 0.500; y₁ is a number in the range from about 0.040to about 0.950; y₂ is a number in the range from 0 to about 0.20; and zis a number in the range from about 0.01 to about 0.5; (x+y₁+y₂+z)=1;and x<(y₁+y₂).
 6. The method of claim 4, further comprising forming asecond slurry of the second phosphate glass composition by combining thesecond phosphate glass composition with a second carrier fluid, whereinapplying the sealing layer of the second phosphate glass composition onthe base layer comprises spraying or brushing the second slurry of thesecond phosphate glass composition on the base layer.
 7. The method ofclaim 6, wherein the second slurry further comprises an aluminumphosphate.
 8. The method of claim 1, comprising forming a first slurryof the first phosphate glass composition by combining a pulverized firstphosphate glass matrix with a first carrier fluid, the plurality ofgraphene nanoplatelets, and the boron nitride additive.
 9. The method ofclaim 1, wherein prior to applying the base layer of the first phosphateglass composition to the carbon-carbon composite structure, apretreating composition is applied to the outer surface of thecarbon-carbon composite structure, the pretreating compositioncomprising one of a phosphoric acid and an acid phosphate salt, an onealuminum salt, and an additional salt, and wherein the carbon-carboncomposite structure is porous and the pretreating composition penetratesat least some of a plurality of pores of the carbon-carbon compositestructure.
 10. The method of claim 1, wherein prior to applying the baselayer of the first phosphate glass composition to the carbon-carboncomposite structure, a first pretreating composition is applied to theouter surface of the carbon-carbon composite structure, the firstpretreating composition comprising aluminum oxide and water, whereinafter heating the pretreating composition, a second pretreatingcomposition comprising one of a phosphoric acid and an acid phosphatesalt, and an aluminum salt is applied to an outer surface of the firstpretreating composition, wherein the carbon-carbon composite structureis porous and the second pretreating composition penetrates at leastsome of a plurality of pores of the carbon-carbon composite structure.